In the prior art, a linear ground penetrating radar array (GPR) is swept across an area of ground. The GPR gathers data from each element of the array periodically as it traverses the ground. The traversed motion is usually achieved by rigidly mounting the array to a vehicle or cart. The GPR is kept at some nominal height from the ground. Data collected from each element as it traverses the ground is used to create a 3-dimensional image of the ground surface and the anomalies beneath the ground surface. The delay time of each of the reflections occurring in each data element corresponds to a distance from the corresponding antenna element.
As the array is traversed over the ground, each radar antenna element is activated, yielding a one-dimensional A-scan. When all radar elements in the linear array are activated, a 2-dimensional image of the ground under the array can be recreated, yielding a radar B-scan. As the array is moved, B-scans are collected in some uniform manner, often based on the array moving some fixed distance. This yields a 3-dimensional data cube. It is desirable to move the array in a linear manner over the ground in order to avoid distorting the image of any sub-surface anomalies. However, the dynamics of the vehicle carrying the linear GPR array can preclude such a linear collection. Vehicle dynamics can introduce height variations and cause the absolute elevation of the array elements to vary from one B-scan to the next. In order to avoid distortion in the resulting image and to accurately map the contour of the ground, it is desirable to correct for these variations.
One possible correction is to detect the location of the ground and compensate for any elevation variation in the GPR array by aligning the ground reflections from one B-scan to the next. This method of compensation operates on the assumption that the ground is flat. Any variations in the ground surface elevation results in corresponding distortions in the image of any subsurface anomaly. Often over uneven ground it is desirable to obtain an accurate un-distorted image of the anomaly in order to identify and characterize it. If height changes due to radar elevation and height changes due to ground elevation variation can be differentiated, compensation can be applied to the resulting data cubes which will minimize distortion of the image. Accurate inertial navigation systems (INS) or differential GPS systems may accomplish similar objectives. However, INS and GPS systems can drastically increase the total cost of a system.
Needs exist for an improved method for detecting elevation changes of a radar array and for differentiating between height changes due to radar elevation and height changes due to ground elevation variation.